The present invention relates to an elementary circuit antenna for a network for sending and/or receiving telecommunication signals, capable of radiating polarization-duplexed radio-electrical fields, i.e. capable of operating with dual polarization, and of operating in two frequency bands.
Such an antenna is designed to operate in the first frequency band of a cellular radio telecommunications network conforming to the DCS-1800 standard and in a second band of frequencies for a cellular radio communications system conforming to the GSM-900 standard.
In the paper xe2x80x9cMultifrequency Operation of Microstrip Antennas Using Aperture Coupled Parallel Resonatorsxe2x80x9d by Frederic Croq and David M. Pozar, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, Vol. 40, No. 11, November 1992, pages 1367 to 1374, a microstrip antenna includes two dielectric layers with a ground conductor plane between them and a microstrip microwave feed line and a radiating element arranged on respective outside faces. The radiating element includes a plurality of parallel conductive strips of different lengths and extending perpendicularly to a coupling slot formed in the ground conductor plane. As a general rule, 2 N conductive strips are distributed symmetrically about an axis transverse to the slot and thus constitute 2 N dipoles excited symmetrically by the slot and resonating at N frequencies.
In the paper xe2x80x9cDual-Frequency and Broad-Band Antennas with Stacked Quarter Wavelength Elementsxe2x80x9d by Lakhdar Zaxc3xafd et al., IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, Vol. 47, No. 4, April 1999, pages 654 to 660, a dual band antenna is formed of two stacked quarter-wave elements short-circuited along opposite lateral planes or a common lateral plane.
The antennas described in the above two papers offer bandwidths of less than 10% for a standing wave ratio less than 1.5 and for mean frequencies of the order of a few Gigahertz.
An object of the present invention is to provide a printed antenna capable of operating in two frequency bands with a standing wave ratio of less than 1.5 over more than 10% of the bandwidth in each band and with electromagnetic field polarizations that are crossed in the two bands so that signals in one band do not interfere with signals in the other band.
A printed circuit antenna in accordance with the invention includes, as described in European patent No. 484,241 filed by the assignee and in the paper xe2x80x9cDual-Polarization Slot-Coupled Printed Antennas Fed by Striplinexe2x80x9d by P. Brachat et al., IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, Vol. 43, No. 7, July 1995, pages 738 to 742, a first dielectric layer, a second dielectric layer, a first microwave feed line having a first microwave strip disposed on an outside face of the first layer and a ground conductor plane disposed between the first and second layers, and a first radiating element disposed on another face of the second layer and including a plurality of first narrow conductive strips perpendicular to a first coupling slot in the conductor plane for coupling the first feed line to the first radiating element.
Based on the above single polarization printed antenna structure with single band operation, the invention provides an improvement whereby an antenna according to the invention includes a second microwave feed line constituted by a second microstrip disposed on the outside face of the first layer perpendicularly to the first microstrip and by said ground conductor plane, a third dielectric layer having a face disposed against the first radiating element, and a second radiating element disposed on another face of the third layer and including a plurality of second narrow conductive strips crossing perpendicularly by superposition the first conductive strips and extending perpendicular to a second coupling slot in the ground conductor plane for coupling the second feed line to the second radiating element.
Thanks to the second radiating element, the antenna according to the invention operates at two different frequencies with respective orthogonal polarizations. For example, the first element radiates in the frequency band of the DCS 1800 radiotelephone network and the second element radiates in the frequency band of the GSM radiotelephone network. The antenna in accordance with the invention has the same bandwidth performance as the prior art antenna described in European Patent No. 484,241 and the same polarization purity thanks to the concept of a grid formed by the first strips and the second strips to constitute the first and second radiating elements. The perpendicular arrangement of the first strips relative to the second strips avoids any interference caused by the polarized radio-electrical field emitted by the first element relative to the polarized radio-electrical field emitted by the second element.
What is more, the printed circuit antenna according to the invention is compact because the two feed lines have a common ground conductor plane including the two coupling slots and microstrips disposed on the same face of the first dielectric layer, and the strips of the radiating elements are superposed where they cross over.
The invention concerns an array of antennas including a plurality of first antennas whose first shorter strips are parallel to each other and whose second strips are also parallel to each other.
For this array of antennas to have crossed polarizations in each of the two frequency bands, it includes a plurality of second antennas whose shorter first strips and second strips extend coplanar and respectively perpendicular to the first strips and to the second strips of the first antennas.
The first antennas are divided into columns which are interleaved two by two with columns into which the second antennas are divided.